1. Field of the Invention
The present invention relates to a method for producing L-amino acids using bacteria. L-amino acids have many useful and various applications, including as additives in seasonings, food additives, feed additives, chemical products, and drugs.
2. Brief Description of the Related Art
L-amino acids such as L-threonine and L-lysine are industrially produced by fermentation methods using L-amino acid-producing bacteria such as Escherichia bacteria. Examples of L-amino acid-producing bacteria can include bacterial strains isolated from nature or artificially mutated strains, as well as recombinant strains obtained by modifying the bacteria so that the activities of L-amino acid biosynthetic enzymes are enhanced. Methods for producing L-threonine can include those disclosed in JP 05-304969 A, WO 98/04715, JP 05-227977 A, and US 2002/0110876 A. Methods of producing L-lysine include those disclosed in JP 10-165180 A, JP 11-192088 A, JP 2000-253879 A, and JP 2001-057896 A.
In fermentative production of an L-amino acid, sugars such as glucose, fructose, sucrose, molasses, and starch hydrolysate are generally used as sources of carbon.
Clark et al. reported that an Escherichia coli wild-type strain can grow in a medium containing long-chain fatty acids (12 or more carbon atoms) as the sole carbon source (Clark, D. P. and Cronan Jr., J. E. 1996. p. 2343-2357. In F. D. Neidhardt (ed.), Escherichia coli and Salmonella Cellular and Molecular Biology/Second Edition, American Society for Microbiology Press, Washington, D.C.). Weeks et al. reported that an Escherichia coli wild-type strain can grow in a medium containing palmitic acid or oleic acid as the sole carbon source (Weeks, G., Shapiro, M. Burns, R. O., and Wakil, S. J. 1969. Control of Fatty Acid Metabolism I. Induction of the Enzymes of Fatty Acid Oxidation in Escherichia coli. J. Bacteriol. 97:827-836). However, the solubility of fatty acids is known to be extremely low, and Vorum et al. reported that the solubility of oleic acid is 0.0003 g/l or less, and that of palmitic acid is 0.00000003 g/l or less, whereas the solubility of lauric acid is 0.1 g/l or more (Vorum, H., Brodersen, R., Kragh-Hansen, U., and Pedersen, A. O, Solubility of long-chain fatty acids in phosphate buffer at pH 7.4. 1992. Biochimica et Biophysica Acta, Lipids and Lipid Metabolism 1126: 135-142).
Therefore, there are very few examples of production of substances by a direct fermentation method using fatty acids as the sole carbon source, and there have been no reports of production of an L-amino acid by such methods. Furthermore, when fatty acids are employed as the sole carbon source, the concentration of the fatty acids is typically about 1 g/l. For example, JP 11-243956 A discloses an example of production of polyester, where the culture medium contains only 2 g/l lauric acid as the carbon source.